Halogen lamps have an energy distribution closely analogous to that of perfect radiators, and thus exhibit excellent color rendering properties. Furthermore, depending on the magnitude of supplied power to a halogen lamp, the color temperature of light emitted from the halogen lamp can be changed, and the halogen lamp is thus used as a visible light source. However, the halogen lamps have problems, such as producing infrared emission and thus becoming at very high temperatures, requiring a reflector plate for inhibiting infrared radiation, having a life shorter than that of LEDs, having large power consumption. Thus, developments of white-light light-emitting device with small heat generation using longer-life light-emitting diodes (LEDs) have been performed.
In PTL 1 (Japanese Unexamined Patent Application Publication No. 2009-224656), a light-emitting device is disclosed which includes a base body having a recessed part where a plurality of tilted surfaces tilted in direction opposing to one another are formed on a bottom surface, light-emitting elements installed on the respective tilted surfaces, and wavelength converting members provided so as to cover the respective light-emitting elements to convert light emitted from the respective light-emitting elements into lights with wavelengths different from one another.
In PTL 2 (Japanese Unexamined Patent Application Publication No. 2011-159809), a white-light light-emitting device is disclosed which includes a first white-light generating system formed of ultraviolet or violet LED chips and phosphors to generate first white light and a second white-light generating system formed of blue LED chips and phosphors to generate second white light. The first and second white-light generating systems are spatially separated, the first white light has a color temperature lower than that of the second white light, and the white-light light-emitting device is configured to be able to emit mixed light including the first white light and the second white light.
In PTL 3 (Japanese Unexamined Patent Application Publication No. 2011-222723), a light-emitting device is disclosed which has a light source unit with a resistor connected in series to a first LED so that a ratio of a luminous flux of the first LED and a luminous flux of a second LED is not constant with a change in output voltage of a power source device.